Use subscription-manager list to check for RHSM registration status

[anjannath]

use subscription-manager list instead of subscription-manager version
In an unregistered system the o/p subscription-manager version

$ sudo subscription-manager version
server type: Red Hat Subscription Management
subscription management server: 2.2.3-1
subscription management rules: 5.26
subscription-manager: 1.20.11-1.el7_5

o/p of subscription-manager list

$ sudo subscription-manager list
+-------------------------------------------+
    Installed Product Status
+-------------------------------------------+
Product Name:   Red Hat Enterprise Linux Server
Product ID:     69
Version:        7.5
Arch:           x86_64
Status:         Unknown
Status Details: 
Starts:         
Ends:           

[LalatenduMohanty]

Resolved via #2527